正则表达式是一种字符模式，用于在查找过程中匹配制定的字符。

元字符通常在Linux中分为两类：

Shell元字符，由Linux Shell进行解析；
正则表达式元字符，由vi/grep/sed/awk等文本处理工具进行解析；
正则表达式一般以文本行进行处理，在进行下面实例之前，先为grep命令设置–color参数：

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alias grep='grep --color=auto'

这样每次过滤出来的字符串都会带色彩了。

在开始之前还需要做一件事情，就是创建一个测试用的

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$ cat re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.

文件内容摘录自<<UNIX/SHELL范例精解第四版>>

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$ cat linux.txt
Linux is a good 
god assdxw bcvnbvbjk
greatttttt  wexcvxc
operaaaating  dhfghfvx
gooodfs awrerdxxhkl
gdsystem awxxxx
glad
good

正则表达式元字符

元字符 功能
^ 以什么开头
$ 以什么结尾
. 匹配一个字符
* 匹配0个或多个
[] 匹配集合中的
[x-y] 匹配集合范围内的
[^ ] 匹配不在集合中的
\ 转义
  • 特殊的元字符
元字符 功能 实例 怎么匹配
< 以什么开头 ‘<love’ 匹配以love开头的所有行
> 以什么结尾 ‘love>‘ 匹配love结尾的所有行
\(..\) 标签匹配以后使用的字符 ‘(love)able \1er’ 用位置\1\2引导前面做好的标签，最大支持9个
x\{m\} or x\{m,\} or x\{m,n\} 重复字符x，m次，至少m次，至少m且不超过n次 o\{5,10\} o字符重复5到10次的行
  • 扩展的正则表达式
元字符 说明
+ 重复前一个字符一个或一个以上
? 0个或者一个字符
丨 表示或，查找多个字符串
（） 分组过滤匹配

实操

  • 匹配以love开头的所有行
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$ grep '^love' re-file
love, how much I adore you. Do you know
  • 匹配love结尾的所有行
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$ grep 'love$' re-file
clover. Did you see them?  I can only hope love.
  • 匹配以l开头，中间包含两个字符，结尾是e的所有行
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$ grep 'l..e' re-file
I had a lovely time on our little picnic.
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
  • 匹配0个或多个空行，后面是love的字符
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$ grep ' *love' re-file
I had a lovely time on our little picnic.
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
  • 匹配love或Love
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$ grep '[Ll]ove' re-file  # 对l不区分大小写
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
  • 匹配A-Z的字母，其次是ove
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$ grep '[A-Z]ove' re-file
Lovers were all around us. It is springtime. Oh
  • 匹配不在A-Z范围内的任何字符行，所有的小写字符
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$ grep '[^A-Z]' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.
  • 匹配love.
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$ grep 'love\.' re-file
clover. Did you see them?  I can only hope love.
  • 匹配空格
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$ grep '^$' re-file
  • 匹配任意字符
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$ grep '.*' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.
  • 前面o字符重复2到4次
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$ grep 'o\{2,4\}' re-file
groove.
  • 重复o字符至少2次
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$ grep 'o\{2,\}' re-file
groove.
  • 重复0字符最多2次
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$ grep 'o\{,2\}' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.
  • 重复前一个字符一个或一个以
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$ egrep "go+d" linux.txt
Linux is a good
god assdxw bcvnbvbjk
gooodfs awrerdxxhkl
good
  • 0个或者一个字符
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ansheng@Ubuntu:/tmp$ egrep "go?d" linux.txt
god assdxw bcvnbvbjk
gdsystem awxxxx
  • 或，查找多个字符串
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$ egrep "gd|good" linux.txt
Linux is a good
gdsystem awxxxx
good
  • 分组过滤匹配
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$ egrep "g(la|oo)d" linux.txt
Linux is a good
glad
good

原作者：安生
本文转自:https://blog.ansheng.me/article/examples-of-linux-regular-expressions